Method for on-mold coating molded articles with a coating powder as a liquid gel coat replacement

ABSTRACT

Method for on-mold surface coating fiberglass-reinforced molded articles during their manufacture with environmentally friendly and physiologically safe thermosetting unsaturated polyester on-mold coating powders which serve as replacements for liquid gel coats. The thermosetting coating powders employed are adapted to cure at low temperatures to avoid causing thermal damage to the heat sensitive plastic molds which must be reused over and over again, and to cure in the presence of atmospheric oxygen to enable over coating with liquid fill resins and fiberglass, which constitute the bulk of the finished article, without having the fill resins bleed through the powder coating film and detrimentally affect the overall quality of the surface finish.

FIELD OF THE INVENTION

[0001] This invention relates to the manufacture of molded articles fromthermosetting resins with or without glass fiber reinforcement. Moreparticularly, this invention relates to a method for on-mold coating thesurface of molded articles during their manufacture with powderedthermosetting resins that serve as replacements for liquid gel coats, tomolded articles having surface coatings so formed thereon, and topowdered thermosetting resins adapted for on-mold coating.

BACKGROUND OF THE INVENTION

[0002] Liquid gel coat on-mold coating is a known technique fordecorating or protecting the surface of a molded article formed fromthermosetting resins, whether or not reinforced with glass fibers. Inthis technique, a liquid gel coat, which becomes the outer surface orskin of the molded article, is sprayed onto the interior wall of afemale mold prior to molding the part. After the gel coat layer hashardened sufficiently, one or more liquid thermosetting fill resinlayers, with or without glass fiber reinforcement, which constitute thebulk of the finsihed article, are then laid up or sprayed up over thegel coat. Layers are added and allowed to cure as needed to build thearticle to the desired thickness. After the cure has advancedsufficiently and the gel coat and fill resin layers are integral, thefinished coated article is released from the mold which is later reused.

[0003] On-mold coating as described above is distinguished frompost-mold coating processes, in which the fill resin is molded beforethe coating is introduced in the mold, and from conventional decoratingoperations, in which the fill resin is molded and cured in the mold,then released from the mold and decorated with a coating powder or otherfinish. On-mold coating is also distinguished from in-mold coatingprocesses, in which matching molds are utilized and the coating and fillresin are cured together in a closed molding environment under heat andpressure.

[0004] There are a number of drawbacks associated with the use of liquidgel coats during on-mold coating. For instance, liquid gel coats arehard to apply uniformly to the mold surface and overspray must becollected and removed as hazardous waste. Consequently, the transferefficiency of liquid gel coats is extremely poor (i.e., about 38%).Liquid gel coats also contain alarmingly high levels of volatile organicsolvents or crosslinking liquid monomers, such as liquid styrenemonomers, which tend to flash away when sprayed on the mold, thuschanging the coating formulation, creating bubbles, undesired porosity,and other irregularities in the surface coating, and generating VOC's atunsafe levels, making it necessary to contain and collect the vapor ofvolatile ingredients. Also, this manner of operation results in longcycle times as the gel coat must be allowed to harden for several hoursbefore application of the fill resin. Lastly, the resulting surfacecoating, despite being very thick is insufficiently resistant toscratching, cracking, impact, light, heat, moisture, salinity,weathering and solvents.

[0005] In view of the foregoing drawbacks, recent emphasis has beenplaced on finding a suitable replacement for liquid gel coats. Highsolids and water-borne liquid coatings have been tried, but they fail todeliver the needed performance. Thermosetting coating powders have alsobeen proposed. Coating powders have a number of advantages over liquidgel coats. For instance, they are essentially free of volatile organicsolvents, and, as a result, give off little, if any, VOC's to theenvironment when cured. In addition, coating powders improve workinghygiene, as they are in dry, free-flowing, solid form and have no messyliquids associated with them to adhere to workers' clothes and coatingequipment. They are relatively non-toxic and in the event of a spill areeasily swept up without requiring special cleaning and spill containmentsupplies. Lastly, oversprayed powders can be recycled during the coatingoperation and recombined with the original powder feed, leading to veryhigh (i.e., almost 100%) transfer efficiencies and minimal wastegeneration.

[0006] However, thermosetting coating powders are not without problems.Traditionally, they have not been suited for application onto heatsensitive substrates, including plastic molds, such as the unsaturatedpolyester molds normally employed in the manufacture of molded articlesdescribed above, due to the rather high temperatures demanded tomelt-flow and cure the powders. Because such molds are rather expensiveand must be reused over and over again, thermal damage caused by curingat temperatures above their softening point or plastic deformationtemperature cannot be tolerated. While a number of lower temperaturecuring thermosetting coating powders based on unsaturated polyesterresins have been proposed for on-molding coating purposes, they alsohave suffered from significant drawbacks, such as an inability tosufficiently cure on the surface in an open air molding process, makingsuch powders useful only in a closed molding environment, or aninability to resist blocking or sintering at room temperature, renderingsuch powders physically unstable and virtually unusable after prolongedstorage.

[0007] U.S. Pat. No. 4,316,869 (Van Gasse) teaches a method for on-moldcoating of molded articles, particularly fiberglass-reinforced boathulls, with thermosetting coating powders. Specifically disclosed arepowdered unsaturated polyester resin formulations containing anunsaturated polyester resin, a copolymerizable cross-linking diallylester prepolymer, a cure initiator, along with other common additives.Also required therein is a high-boiling, copolymerizable cross-linkingmonomer, in particular di- or tri-functional allyl-containing monomers,such as triallyl cyanurate and triallyl isocyanurate. Yet, there aredisadvantages to using cross-linking monomers. For instance, suchmonomers are typically liquids or waxy (low melting) solids at roomtemperature which have only limited use in coating powders. Whenemployed beyond trace amounts, they tend to dramatically lower the glasstransition temperature (Tg) of the formulation, causing the powders toblock or sinter during storage and making them virtually impossible tometer and spray during commercial coating operations. Conversion of suchmaterials into higher melting solids is rather expensive andtime-consuming.

SUMMARY OF THE INVENTION

[0008] It is, therefore, an object of this invention to provide for themanufacture of molded articles formed from thermosetting resins, with orwithout fiber reinforcement, that avoids the foregoing drawbacks.

[0009] More particularly, it is an object of this invention to providemethods for on-mold coating the surface of molded articles formed fromthermosetting resins during their manufacture with low temperature curethermosetting coating powders, molded articles having surface coatingsso formed thereon, and low temperature cure thermosetting coatingpowders adapted for use in said on-mold coating methods, that avoid theforegoing drawbacks.

[0010] In accordance with one aspect of this invention, there areprovided methods for on-mold coating the outer surface of a moldedarticle formed from thermosetting resins, with or without glass fiberreinforcement, on a heat sensitive (i.e., plastic) female mold surfacewithout damaging the mold, using a low temperature cure thermosettingunsaturated polyester coating powder, which methods comprise: a)providing one of the low temperature cure thermosetting unsaturatedpolyester coating powder compositions described below; b) applying thecoating powder, which becomes the outer surface of the molded article,onto the mold surface, preferably while the mold surface is sufficientlyhot to cause the powder particles to melt and flow and spread out overthe mold surface and form a substantially continuous film at least alongthe mold interface; c) heating the powder coated mold surface to meltand flow any solid powder particles and cause the resulting monolithiccoating film to cure, preferably to completion; d) applying a compatibleliquid thermosetting fill resin, with or without glass fiberreinforcement, which constitutes the bulk of the molded article, ontothe cured coating powder film and allowing the cure of the fill resin toadvance sufficiently until the powder coating and fill resin areintegral; and, e) removing the molded article from the mold as thefinished coated article. In the aforesaid method, the coating powderapplication and curing steps b) and c) are preferably carried out in anopen air environment, i.e., while the mold is opened and exposed toambient conditions.

[0011] In accordance with another aspect of this invention, there areprovided thermosetting coating powders adapted for said on-mold coatingmethods, which powders are melt extrudable, storage stable, readilyfluidizable, not only curable in an open air environment but also atsufficiently low temperatures to not cause damage to plastic molds, andfurthermore are capable of providing a surface coating that isexceptionally smooth, uniform, glossy and attractive in appearance withlittle or no surface porosity, resistant to scratching, impact,cracking, staining, light, heat, moisture, salinity, weathering, andsolvents, and one that forms a very strong bond with the thermosettingfill resin, wherein the powders consist essentially of a reactivefilm-forming blend in particulate form of: a) an ethylenicallyunsaturated polyester resin; b) a copolymerizable cross-linkingethylenically unsaturated prepolymer; c) a thermal initiator; d)optional cure catalyst; and, e) a mold release agent, with the provisothat: I) the particulate blend is essentially free of anycopolymerizable cross-linking ethylenically unsaturated monomers; and,preferably with the further proviso that: ii) either the unsaturatedpolyester resin contains at least one active hydrogen atom, or saidparticulate blend further consists essentially of a photoinitiatoralongside the thermal initiator, or both. In the above on-mold coatingmethod, if the coating powder includes a photoinitiator, prior to orfollowing heating step c), the coating film is exposed to sufficientultraviolet or ionizing radiation to effect radiation curing along thesurface exposed to air.

[0012] A first preferred on-mold coating powder useful in this inventionconsists essentially of a particulate blend of a) an unsaturatedpolyester resin containing active hydrogen atoms obtained by thecondensation of an ethylenically unsaturated dicarboxylic acid (oranhydride), e.g., maleic anhydride or fumaric acid, and a diolpossessing active hydrogen atoms, e.g., 1,4-cyclohexane dimethanol, toreduce air inhibition of cure at the exposed surface and improve flowout behavior at low temperatures, along with minor amounts of aromaticdicarboxylic acid (or anhydride) and aromatic diols, e.g., a combinationof phthalic anhydride and hydrogenated bisphenol A, respectively, toraise the Tg of the resin such that the powdered blend remainsphysically stable and solid at room temperature, together with b) across-linking difunctional allyl ester prepolymer, e.g., iso-diallylphthalate, c) a peroxide thermal initiator, e.g., a peroxy ketal, d) aredox catalyst, e.g., a cobalt salt, and e) a mold release agent, andthe usual additives.

[0013] A second preferred on-mold coating powder useful in thisinvention consists essentially of a particulate blend of a) anunsaturated polyester resin containing maleate or fumarate unsaturation,b) a cross-linking difunctional vinyl ether urethane prepolymer, c) aperoxide thermal initiator, e.g., a peroxy ketal, d) a redox catalyst,e.g., cobalt salt, e) a mold release agent, and f) a photoinitiator,e.g., a benzyl ketal, acyl phosphine, or aryl ketone, together with theusual additives.

[0014] In yet another aspect of this invention, there are providedmolded articles, with or without fiber reinforcement having surfacecoatings formed thereon by the aforesaid on-mold coating methods.

[0015] The various objects, features and advantages of this inventionwill become more apparent from the following description and appendedclaims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Throughout this specification, all parts and percentagesspecified herein are by weight unless otherwise stated. Also, in thefollowing description of the coating powders used to form the outer skinof the molded product, component a) (the unsaturated polyester resin)and component b) (the copolymerizable cross-linking unsaturatedprepolymer) are herein considered to be the “resin” and equal to 100parts. Levels of other components are calculated as parts relative to100 parts of the resin (abbrev. “phr”).

On-Mold Coating Powders

[0017] The coating powders useful in the practice of this invention arelow temperature cure powdered thermosetting unsaturated polyester resinformulations adapted to be applied to a mold surface and form an outerskin on a resinous body molded thereon without damaging the mold. Thesecoating powders consist essentially of a reactive film-formingparticulate blend of an ethylenically unsaturated polyester resin, across-linking ethylenically unsaturated prepolymer, a thermal initiator,optional cure catalyst, and a mold release agent, with the proviso thatthe particulate blend is essentially free of any cross-linkingethylenically unsaturated monomers. In order to achieve sufficientsurface cure in an open air molding environment as contemplated in thisinvention, the powders are preferably further characterized in thateither the unsaturated polyester resin possesses an active hydrogenatom, or the particulate blend further consists essentially of aphotoinitiator alongside the thermal initiator, or both. It isparticularly important for any unsaturated polyester coating powderemployed in an open atmosphere on-mold coating process to be able toachieve complete cure along the inner surface of the coating exposed toair, as this prevents the liquid fill resin from bleeding through thepowder coating film and marring the appearance of the outer surfacefinish.

[0018] The unsaturated polyester resins useful in the practice of thisinvention can be obtained in a conventional manner, such as bycondensation of one or more di- or polyfunctional carboxylic acids ortheir anhydrides, preferably dicarboxylic acids or their anhydrides,with one or more di- or polyfunctional alcohols, preferably dihydricalcohols. The ethylenic unsaturation is usually supplied by the acid,although it is possible to supply it instead through the polyol. Theunsaturation can be provided in the polymer backbone or at the end ofthe chain. If it is supplied in the backbone, ethylenically unsaturateddi- and polyfunctional acids or their anhydrides useful for this purposeinclude maleic anhydride, fumaric acid, itaconic anhydride,tetrahydrophthalic anhydride, nadic anhydride, dimeric methacrylic acid,etc. Maleic anhydride, fumaric acid, or their mixtures are generallypreferred because of economic considerations. It should be understoodthat whether acids or anhydrides are listed, any of these forms arecontemplated for use herein. If unsaturation is supplied at the chainend, ethylenically unsaturated monofunctional carboxylic acids (or theiresters) are employed, for example, acrylic acid, methacrylic acid, etc.

[0019] Often, minor amounts of saturated aliphatic and aromatic di- andpolyfunctional carboxylic acids or their anhydrides are employed inconjunction with the ethylenically unsaturated acids to reduce thedensity of the ethylenic unsaturation and provide desired chemical andmechanical properties. Examples of suitable saturated aliphatic andaromatic polyfunctional acids (or anhydrides thereof) employed to tailorthe properties of the resin (e.g., to raise the Tg of the resin) includeadipic acid, succinic acid, sebacic acid, phthalic anhydride,isophthalic acid, terephthalic acid, dimethylterephthalate,dimethylisophthalate, tetrahydrophthalic acid, hexahydrophthalic acid,cyclohexane dicarboxylic acid, dodecane dicarboxylic acid, trimelliticacid, pyromellitic anhydride, etc.

[0020] As described above, to enable surface curing of the exposedsurface of the coating film in an open air molding environment, it isdesirable that the polyester resin contain an active hydrogen atom inits backbone. The term “active hydrogen” used herein means a hydrogenatom that is readily abstracted by free radicals and participates in thecuring reaction. The active hydrogen atoms are typically supplied by thepolyol, although it may instead come from active hydrogen containingacids employed in conjunction with the unsaturated acid. Examples of di-or polyfunctional alcohols useful herein which contain active hydrogenatoms include those with allylic, benzylic, tertiary alkyl, orcyclohexyl hydrogen atoms. These active hydrogen atoms are readilyabstracted during free radical-induced curing and form correspondingallylic, benzylic, cyclohexyl, and tertiary alkyl free radicals, all ofwhich promote curing at the exposed surface. While not wishing to bebound by theory, it is believed that inclusion of an active hydrogencontaining compound in the unsaturated polyester molecule allows for thegeneration of free radicals which have greater stability and are lesssusceptible to permanent deactivation upon contact with atmosphericoxygen.

[0021] Examples of suitable di- or polyfunctional alcohols possessingactive hydrogens include alcohols having: an allylic hydrogen, such astrimethylol propane monoallyl ether, trimethyol propane diallyl ether,vinyl cyclohexanediol, etc.; a benzylic hydrogen, such as benzenedimethanol, etc.; a tertiary alkyl hydrogen, such as methyl propanediol,butylethyl propanediol, etc.; and, a cyclohexyl hydrogen, such ascyclohexane dimethanol, cyclohexane diol, etc. As mentioned above, it isalso possible to supply the active hydrogen through the carboxylic acid.Examples of suitable di- or polyfunctional carboxylic acids with activehydrogens include carboxylic acids having: a malonyl hydrogen, such asmalonic acid, etc.; or an allylic hydrogen, such as nadic anhydride,tetrahydrophthalic anhydride, dimer acid, etc.

[0022] Often, polyols without active hydrogens are employed in thecondensation reaction in conjunction with a substantial proportion ofactive hydrogen containing polyols to provide desired chemical andmechanical properties. Typically, between about 10 and 100 mole %, andpreferably between about 50 and 100 mole %, of the hydroxylfunctionality relative to the total hydroxyl functionality of monomersused to form the unsaturated polyester resin A) is supplied by activehydrogen containing polyol monomers, the balance being non-activehydrogen containing polyols. Examples of suitable di- or polyfunctionalalcohols that do not contain active hydrogens employed to tailor theproperties of the resin (e.g., to raise the Tg of the resin) includeethylene glycol, diethylene glycol, triethylene glycol, propyleneglycol, neopentyl glycol, butanediol, dodecanediol, hydrogenatedbisphenol A, bisphenol A/propylene oxide adducts, glycerol,trimethylolpropane, trimethylolethane, etc.

[0023] Whether the polyester is acid-functional orhydroxyl-functionalized depends upon the —COOH/—OH ratio of the monomermix. While these saturated functionalities generally do not participatein the curing reaction which proceeds primarily through the unsaturatedgroups, they are often used to achieve desired chemical and mechanicalproperties in the final polymer. If the unsaturated polyester isacid-functional, the acid number is usually about 1 to 80. If theunsaturated polyester is hydroxyl-functional, the hydroxyl number isusually about 5 to 100.

[0024] The unsaturated polyester resin can be formulated to be eithercrystalline (i.e., semi-crystalline) or amorphous resins. Crystallineresins or blends of crystalline and amorphous resins are desirable forforming powder coatings with low melt viscosities and good flow outbehavior at low temperatures. It is well known in the art that certainalcohol and acid monomers impart crystallinity to unsaturatedpolyesters. For example, symmetrically substituted linear monomers orcyclic monomers or their mixtures are generally used to form crystallinepolyesters. Examples of suitable diols that are known to promotecrystallinity include ethylene glycol, butanediol, hexanediol, andcyclohexane dimethanol. Examples of suitable dicarboxylic acids that areknown to do the same include terephthalic acid, adipic acid, dodecanedicarboxylic acid, and cyclohexane dicarboxylic acid.

[0025] Most desirably, the unsaturated polyesters suitable for thepractice of this invention are solid materials substantially above roomtemperature, so that they can be easily formulated into coating powdersthat will not block or sinter during ambient storage. On the other hand,the unsaturated polyesters should have a low enough melt temperaturesand melt viscosities at said temperatures to enable the coating powdersformulated therefrom to melt, flow and readily spread out over theentire mold surface below the deformation temperature of the mold. Itshould be understood that what determines the above properties of thecoating powders is generally the unsaturated polyester resin componentused therein, as this comprises the major portion of the resin.

[0026] The unsaturated polyester resins, therefore, preferably have amolecular weight in the range of about 400 to 10,000, and morepreferably 1,000 to about 4,500, a glass transition temperature (Tg)sufficiently high to prevent sintering at room temperature up to about90-100° F., preferably about 100 to 150° F., and more preferably about105 to 120° F., and a melt viscosity sufficiently low to enable thepowder after melting to fully wet out the mold surface at the desiredmold temperature and form a smooth film thereon with virtually nosurface porosity, preferably a melt viscosity at 175° C. (347° F.) belowabout 5,000 centipoise, and more preferably between about 3,750 to 4,750centipoise. The degree of unsaturation, preferably maleate or fumarateunsaturation, normally present in such polyester resins is preferably inthe range of about 2 to 20 wt. % of the polyester resin, and morepreferably about 4 to 10 wt. %.

[0027] The unsaturated polyester resin is blended with a copolymerizablecross-linking ethylenically unsaturated prepolymer or oligomer whichupon curing reacts with linear polyester chains to cross-link them andthereby impart thermoset properties to the coating. The cross-linkingprepolymers useful in the practice of this invention are preferablydifunctional compounds which are solids at room temperature. Such solidresins generally include prepolymers containing vinyl ether, vinylester, allyl ether, allyl ester, acrylate or methacrylate groups at thechain ends. Examples of suitable prepolymers include allyl esters, suchas diallyl phthalates, iso-diallyl phthalates, and p-diallyl phthalates,which are obtained by the reaction product of allyl alcohol and phthalicanhydride; allyl ethers, such as those obtained by reaction of allylpropoxylate and hydrogenated methylene diisocyanate, etc; vinyl ethers,such as divinyl ether urethanes, including those obtained by thereaction of hydroxybutyl vinyl ether either with diisocyanates,isocyanate-terminated alcohol adducts, or isocyanurates, etc.; and,methacrylates or acrylates, such as methacrylated or acrylatedurethanes, including those formed by the reaction of hydroxyethyl orhydroxypropyl methacrylate or acrylate with diisocyanates, etc. Thecross-linking prepolymers, like the unsaturated polyesters, can beformulated to have either a crystalline or amorphous microstructure.This will depend on choice of monomers employed in the formationreaction, as is well known in the art, and the desired flow out behaviorand final coating properties. It will be appreciated by those skilled inthe art that the amount of unsaturated prepolymer relative to theunsaturated polyester resin will depend on the choice of materialsemployed. Usually, such materials are employed in the necessary amountto allow cross-linking to proceed to completion. In general, thistranslates into less than about 25 wt. % of the resin comprisingcross-linking prepolymer.

[0028] A thermal initiator is employed to generate free radicals andinduce cross-linking of the polyester resin to a thermoset state. Thethermal initiators useful herein are desirably solids at roomtemperature and are preferably selected from peroxide and azo compounds.Examples of suitable peroxide initiators include peroxy ketals, such as1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, diacyl peroxides,such as benzoyl peroxide, peroxy esters, dialkylperoxides, ketoneperoxides, etc., with peroxy ketals being preferred. It is most desiredthat the activity of the initiator be such as to enable curing toproceed below the deformation temperature of the mold, preferably belowabout 325° F., while not causing substantial curing in the extruderduring standard melt processing. It is, therefore, particularly desiredto employ thermal initiators which have a one hour half life betweenabout 105 and 135° F. The amount of thermal initiator employed in thecoating powder composition of the present invention typically rangesbetween about 0.1 and 10 phr, and preferably between about 1 and 5 phr.

[0029] Standard photoinitiators can also be used in conjunction with thethermal initiators for photoactivated (i.e., radiation) curing. Asdescribed above, thermal curing of the powder composition may beassisted along the exposed surface by compounds which form free-radicalsunder photolytic conditions, e.g., upon exposure to sufficientultraviolet radiation or ionizing, e.g., electron beam, radiation. Thisis especially important with the powders based on unsaturated polyestersthat do not contain active hydrogen atoms. As with the thermalinitiators, the photoinitiators should be solid compounds at roomtemperature. Of course, if they are liquids, as with any of the othermaterials employed in the powders, they can be converted to solids byabsorption onto inert filler before use, as is well known in the art.Yet, liquids should be avoided whenever possible. Examples of suitablephotoinitiators include benzoin ethers, benzyl ketals, such as benzyldimethyl ketal, acyl phosphines, such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and aryl ketones, such as 1-hydroxycyclohexylphenyl ketone, etc. The photoinitiators, if included, are generallyemployed in an amount sufficient to enable radiation curing along thesurface of the coating film exposed to air. Typically, this translatesto a range between about 0.1 and 10 phr, and preferably between about 1and 5 phr.

[0030] Accelerators or catalysts, particularly redox catalysts, may alsobe employed in the coating powder to induce the generation of freeradicals and allow the cross-linking reactions to proceed at fasterrates. As redox catalysts, transition metal compounds based on a fattyacid or oil may be employed. Examples of suitable metals include cobalt,manganese, lead, copper, and vanadium. Cobalt-containing compounds,especially cobalt salts of monocarboxylic (i.e., fatty) acids, forexample, cobalt octoate, cobalt neodecanoate, cobalt naphthenate, andcobalt octadecanoate, are most preferred. During curing, at the surfaceof the coating, even the free radicals formed at the active hydrogensites tend to react with atmospheric oxygen to form hydroperoxides(i.e., inactivated peroxide initiators), which caps the free radicalsand halts the curing reaction. Yet, the hydroperoxides so formed, due totheir location, are readily decomposed in the presence of the cobaltsalts to re-initiate the free radical cure, thus allowing the cure toproceed to completion at the surface. The redox catalysts are generallyemployed in the coating powder in amounts of less than about 1.0 phr,and preferably in the range between about 0.1 and 0.5 phr.

[0031] Also contained in the coating powders of this invention areinternal mold release agents or lubricants. These lubricating materialspromote mold parting after curing.

[0032] Examples of suitable mold release agents include metallic soapsof fatty acids, such as zinc stearate, copolymers of organophosphateesters, and modified fatty acids, etc. The mold release agents areemployed in an amount sufficient to enable release of the cured coatingfrom the mold after the molded article is completed. The release agentsare generally employed in the coating powder this invention in a rangebetween about 0.1 and 10 phr, and preferably in a range between about 2and 5 phr.

[0033] As described above, the unsaturated polyester on-mold coatingpowders of this invention are virtually free of any copolymerizablecross-linking ethylenically unsaturated monomers, such as thosepreviously mentioned herein and further described in U.S. Pat. No.4,316,869, the teaching of which is incorporated herein by reference inits entirety. Accordingly, the blocking resistance of these powders issubstantially improved, enabling electrostatic spray application of thepowders on the mold surface and the formation of high quality coatingswith minimal surface imperfections.

[0034] It should be understood that the coating powders of thisinvention may also contain the usual other additives. For instance, thecoating powders may include conventional pigments and/or fillers,typically in an amount up to 120 phr, to impart the desired color andopacity to the coating film, although clear (i.e., unpigmented) coatingsare also possible. Suitable pigments include inorganic pigments, such astitanium dioxide, and organic pigments, such as carbon black, etc.Suitable fillers include calcium carbonate, barium sulfate,wollastonite, mica, china clay, diatomaceous earth, boric acid, lowmolecular weight nylon, etc. Other common additives, such as glosscontrol agents, flow or leveling agents, dry flow additives,anticratering or degassing agents, texturing agents, light stabilizers,ultraviolet absorbers, antioxidants, etc., typically in a total amountof up to about 15 phr, may also be included. Suitable gloss controlagents include polyethylene waxes, oxidized polyethylenes, polyamides,teflons, polyamides, etc; flow control agents include acrylic resins,silicone resins, etc; dry flow additives include fumed silica, aluminaoxide, etc; anticratering or degassing agents include benzoin, benzoinderivatives, low molecular weight phenoxy and phthalate plasticizers,etc; texturing agents include organophilic clays, cross linked rubberparticles, multiple curatives, etc; light stabilizers include hinderedamines, etc. Suitable UV absorbers include benzotriazoles, etc;antioxidants include organophosphites, hindered phenolics, etc.

[0035] The melting temperatures and curing temperatures of the abovepowders will vary somewhat depending on the various ingredientsemployed. However, it is particularly important that the coating powderspossess the ability to melt-flow and readily coalesce into a smooth filmwith little or no surface porosity at temperatures and for times thatare safe for the plastic molds, while at the same time remainingphysically stable under ambient storage conditions and chemicallyunreactive during conventional melt-processing. In accordance therewith,the coating powders useful in the practice of this invention areformulated to be dry, free-flowing solid particulates at ambienttemperatures and exhibit no sintering at temperatures at least up to 90°F., preferably up to about 110° F. In addition, the coating powdersdesirably have a melt temperature (i.e., flow temperature) below about250° F., preferably in the range of about 120 to 160° F., and a curetemperature below about 350° F., preferably in the range of about 250 to300° F., temperatures consistent with application of the coating powdercompositions onto plastic molds.

[0036] Of course cure is time-dependent as well as temperaturedependent; however, a full cure at the above temperatures can beachieved within a commercially reasonable time, for example in about 30minutes or less, preferably in about 15 minutes or less. The preferredpowder coatings of this invention can effect a full cure at betweenabout 250-300° F. in about 5 minutes or less which is safe for most heatsensitive applications. A “full cure” is a degree of curing achieved atwhich additional time at elevated temperature will not improve theproperties of the coating once cooled to ambient temperatures. Forthermosetting coating powders, the level of cure can be measured by thesolvent resistance of the coating. Typically, a fully cured coating willwithstand up to about 50 double rubs using methyl ethyl ketone (MEK)solvent without rubbing through to the coated substrate.

[0037] A double rub is a rub back and forth with a solvent-saturatedswab using normal hand-applied pressure.

Coating Powder Preparation

[0038] The coating powders of this invention are prepared in the usualmanner. First, an intimate mixture is formed by dry blending togetherall of the formulation ingredients in a mixer. The dry blend is thenmelt blended in a mixing extruder with heating above the melting pointof the resin and other ingredients, where necessary, so that theextrudate is a thorough and homogeneous mixture. Extrusion is preferablycarried out at between about 180 and 250° F., to minimize any curing andgelation from taking place in the extruder. Gaseous or supercriticalfluid, e.g., CO₂, may be charged to the extruder to reduce the extrusiontemperatures. The extruded composition is rapidly cooled and solidifiedand then broken into chips. Next, the chips are ground in a mill withcooling, and, as necessary, the particulates are screened and sortedaccording to size. Average particle size desired for electrostaticapplication is generally between about 20 and 60 microns.

Liquid Fill Resins

[0039] Thermosetting liquid fill resins, which constitute the bulk ofthe finished article, useful in the practice of this invention are wellknown in the art. The particular fill resin chosen should have achemistry that is compatible with the coating powder to avoid adhesionproblems in the molding. These problems are manifested as bubblesbetween the fill resin and coating of the finished part, or asinsufficient adhesion between the fill resin and coating. It is,therefore, particularly advantageous to employ unsaturated polyesterliquid fill resin formulations to match the chemistry of the coatingpowders. Such fill resins typically consist of unsaturated polyesterresins and cross-linking monomers, e.g., styrene, along with the usualadditives, such as thermal initiators, hardening accelerators orcatalysts, retardants, thickening agents, and fillers.

Molds

[0040] The present invention contemplates the use of a female mold ofthe type commonly employed in the manufacture of the molded articlesfrom thermosetting resins, with or without glass fiber reinforcement.Most often, heat sensitive plastic molds, e.g., unsaturated polyestermolds, are used which have an inner surface in the shape of the articleto be molded. The molds also usually contain conductive pigments, e.g.,carbon black, blended therein which render their surfaces sufficientlyconductive for electrostatic coating. Since these molds are ratherexpensive and are required to be reused over and over again, the coatingpowder must be able to melt-flow and cure at temperatures below thesoftening point or plastic deformation temperature of the molds. Theplastic deformation temperature of such molds is typically between about375 and 450° F. Significant thermal damage occurring to the mold surfaceduring on-mold coating (e.g., cracking, blistering and warping) cannotbe tolerated, as this will not only detrimentally affect the final shapeof the finished article, but also will affect the overall quality of thesurface finish.

On-Mold Coating Methods and Products

[0041] The method of this invention for forming an on-mold coated moldedarticle begins by providing one of the thermosetting unsaturatedpolyester coating powder compositions described above and a plasticfemale mold having a shape-imparting surface defined by the interiorwall of the mold. In an open atmosphere, particles of the unsaturatedpolyester formulation are applied to the surface of the mold, and thenheated so as to melt the particles, whereupon they flow and readilyspread out forming a substantially continuous and preferably whollycontinuous film lining the mold surface. Preferably, the mold surface ispreheated prior to the deposition of the unsaturated polyesterparticles, to cause the powder particles as they strike the hot mold, toimmediately melt, flow, wet out and coalesce into a substantiallycontinuous coating film that at least lines the mold interface. The moldmay be treated with a mold release agent and/or a conductive wash priorto powder application if so desired.

[0042] In the method above, the initial preheating step is usuallycarried out in a preheat station housing banks of high intensity,short-, medium-, or long-wave infrared (IR) lamps directed over the moldsurface for surface warming only, although conventional convention ovensor combination IR and convection ovens may be used. Medium-wave IR lampsare generally preferred. The final temperature of the mold surfacereached during the preheat should be sufficiently high (but still belowthe mold deformation temperature), such that by the time the mold istransferred from the preheat station to the powder application area, thesurface temperature will not fall below the temperature needed to meltthe powder particles, at least at the mold interface. Time andtemperature of the preheat will vary somewhat depending on the coatingpowders employed.

[0043] For the aforementioned powders, the surface temperature of moldas it leaves the preheat station is preferably about 325° F. Because thetemperature of the room is usually about 70 to 80° F., the mold surfacetemperature will quickly fall to a much lower value than 325° F. by thetime the mold reaches the powder coating area which is preferably ashort distance away. However, as the preheated mold enters the powdercoating station, the mold surface temperature should still be above thetemperature needed to cause the powder particles as they strike the hotmold surface to immediately melt, flow and wet out the entire moldsurface. For the aforementioned powders, the surface temperature of themold immediately prior to powder coating is preferably about 200 to 250°F. Such preheating is advantageous for a number of reasons. For example,preheating enhances initial powder attraction to the mold surface,reduces the time needed to cure the powders, results in a more uniformcure, and most importantly allows for the development of coating filmswith the desired smoothness (i.e., no orange peel) and gloss (i.e., a60° gloss value of about 85 or higher) with minimal surface porosity.While preheating is preferred, the coating powders may be applied to amold surface at ambient temperature followed by post-melt and curing,although less attractive films are generally produced.

[0044] After leaving the preheat station, the mold is preferably movedto a powder spray booth located a short distance away from the preheatstation, wherein the coating powder particles are applied to the hotmold surface by electrostatic spraying. While application byelectrostatic means is preferred, any other conventional powder coatingprocess may be used to apply the powder particles. The powder spraybooth typically houses banks of corona discharge or triboelectric sprayguns and a powder reclaim system. Successive layers are applied asneeded to obtain thicker films. Films having a thickness after curing ofabout 5 to 30 mils are most often used. Powder application can usuallybe effected within 1 to 2 minutes. It should be understood that while itis important to have the powders that strike the mold surface tocompletely melt and coalesce into a continuous coating lining the moldto derive the full benefit of the aforesaid coating powders, due toambient cooling and the cooling effect of powder coating itself, thepowder particles applied over the interface powders may remain unmeltedor partially melted until final curing.

[0045] After powder application, the powder coated mold is then moved toa powder cure station preferably located a short distance away from thepowder spray booth. The powder cure station may be one and the same withthe powder preheat station. In the powder cure station, the mold surfaceis heated again preferably using IR lamps as described above to atemperature sufficient to melt and flow any unmelted powder particlesand cure the resulting monolithic coating film on the mold surface,preferably to completion. Although it is possible to maintain thecoating film in a partially cured state until the fill resin is addedand then cure both resins simultaneously to a final cure, it ispreferred to fully cure the unsaturated polyester film prior to addingthe fill resin to prevent the fill resin from bleeding into the powdercoating film.

[0046] Therefore, in the powder cure station, the powder coated moldsurface is heated to a temperature equal to or above the coating powdercure temperature and below the deformation temperature of the mold andmaintained at that level until a complete powder cure is effected,thereby forming a hardened thermoset coating film on the mold surfacehaving an outer surface (defined herein as the surface against the moldsurface) and an opposed inner surface exposed to an open airenvironment. Time and temperature of the final cure will vary somewhatdepending on the coating powders employed and conditions of use.However, for the aforementioned coating powders, the mold surface ispreferably heated to temperature between about 300 and 350° F. for about2 to 5 minutes to effect full cure.

[0047] If a photoinitiator is employed in the coating powder, thecoating film is additionally exposed for a sufficient time to radiation,such as ultraviolet or electron beam radiation, to enable radiationcuring of the exposed inner surface of the coating film. Ultravioletradiation is generally preferred. Radiation curing, if employed, isusually carried out after powder curing in a radiation cure stationpreferably located a short distance away from the powder cure station.Ultraviolet radiation is typically supplied by medium pressure mercuryor doped mercury vapor lamps, such as Fusion H-, D- and/or V-lamps, fora sufficient time, e.g., between about 1 millisecond and 10 seconds,typically less than about 3 seconds, to activate the photoinitiator andinitiate photopolymerization at the inner surface. Radiation curingcould also be effected immediately after powder application providedthat the applied powder particles have completely melted on the moldsurface.

[0048] Further the method described above, after the powder coating filmhas been cured, the mold is transferred to a molding station, whereinthe inner surface of the cured coating film is contacted at the exposedinterface with a liquid fill resin. The liquid fill resin may be appliedby means of spatulas, brushes, rollers, and sprayers. The pertinenttechniques are known by the names of hand lay-up and spray-up. The handlay-up technique involves placing glass mat or other reinforcingmaterials in the mold and saturating the reinforcement material with thefill resin. In the spray-up technique, a mixture of loose glass fibersand fill resin are sprayed into the mold. Successive layers are addedand allowed to cure as needed to build the molded article to the desiredfinal thickness. This bulk layer may also be formed by a technique knownas resin transfer molding in which dry reinforcement materials areplaced in a mold cavity defined by one or more mold surfaces and liquidfill resin is then injected into the cavity to form the molded product,sometimes under vacuum.

[0049] After the cure of the fill resin layer has advanced sufficientlyand the coating film and fill resin are integral across their interface,the shaped article can be removed from the mold. Before or afterremoval, application of other layers consisting of materials of adifferent kind, for example, fiber reinforced cement, foamed polymer, orcombination of both, on the fill resin layer is also possible. When themolded product is removed from the mold, the coating powder film definesthe outer surface of the molded body with complete faithfulness to themold configuration.

[0050] In summary, this invention provides a method for on-moldingcoating molded articles formed from thermosetting resins, with orwithout fiber reinforcement, with thermosetting coating powders in anopen atmosphere, surprisingly without causing thermal damage to the heatsensitive molds (e.g., cracking, blistering, warping, etc.) duringmelting and curing, or without producing inferior surface coatings thatlack the desired non-porosity, smoothness, gloss, glamour, luster,uniformity, intercoat adhesion, and/or resistance to scratching, impact,cracking, light, heat, moisture, salinity, weathering and solvents. Whatmakes such an on-mold coating method possible is that the thermosettingcoating powders employed are uniquely formulated to melt, flow out, andcoalesce into a smooth film and attain full cure, even along the surfaceexposed to air, on the molds at extraordinarily low temperatures and/orrapid speeds, while still being storage stable and melt extrudable.

[0051] This invention will now be described in greater detail by way ofspecific examples.

EXAMPLE 1 Preparation of Unsaturated Polyester Resin Containing ActiveHydrogen Atoms

[0052] This is an example of an unsaturated polyester resin found to beespecially useful in the practice of this invention: 0.85 mole (122.4 g)of 1,4-cyclohexane dimethanol was charged into a 0.5 liter resin kettlefitted with a partial condenser, total condenser, stirrer, nitrogeninlet, and temperature controller. While introducing a stream ofnitrogen at rate of 25-30 ml/min and stirring, the temperature wasraised to 257° F. (125° C.). Thereafter, 0.6 mole (88.8 g) of phthalicanhydride, 0.5 mole (58 g) of fumaric acid, 0.5 mole (36 g) ofhydrogenated bisphenol A, and 50 ppm of 4-methoxy phenol (antioxidant)were added to the kettle. Still under agitation and nitrogen sparge, thetemperature was slowly raised to 356° F. (180° C.) while the water ofesterification was collected. When 85-90% of the theoretical distillatehad been collected, the nitrogen sparge rate was increased to 200ml/min. Viscosity and acid value of the resin were checked periodicallyuntil the desired values were obtained. The amorphous resin was thendischarged into a pan, cooled and ground into flakes. Multiple runs weremade and the resins had properties within the ranges provided in thetable below. Properties Example 1 Glass Transition Temperature (Tg) 42-47° C. Melting Point  52-57° C. Acid Number (mg KOH/g resin)  47 ICIviscosity @ 175° C. (350° F.) 3750-4750 cps Molecular Weight (Mn)1700-1850

EXAMPLE 2 Preparation of Unsaturated Polyester On-Mold Coating Powders

[0053] The following ingredients were blended together in the givenmanner and amounts to form three different on-mold coating powderformulations (A, B, C) of this invention. Parts By Weight Ingredients AB C DRY BLEND IN KNEADER UNTIL HOMOGENEOUS Unsaturated Polyester (fromExample 1) 95 Pioester 277-FLV (Unsaturated Polyester)¹ 95 IsodiallylPhthalate (Diallyl Ester 5 5 Prepolymer) Lupersol 231 XL (PeroxideInitiator)² 4.5 4.5 2 Uralac XP3125 (Unsaturated Polyester)³ 80 UralacZW-3307 (Divinyl Ether 20 Prepolymer)⁴ Surfonyl 104-S (Flow Agent)⁵ 1 11 Modaflow 2000 (Acrylic Flow Agent)⁶ 1 1 1 Moldwiz P-66 (ReleaseAgent)⁷ 3 3 3 Cobalt Neodecanoate (Redox Catalyst)⁸ 0.1 0.1 0.2 TR 93TiO₂ (Pigment)⁹ 20 20 20 R-8098 Red (Iron Oxide Pigment)¹⁰ 0.01 0.010.01 Raven Black 22 (Carbon Black Pigment)¹¹ 0.014 0.014 0.014 MELTBLEND IN TWIN SCREW EXTRUDER AT 180° F. COOL EXTRUDATE AND BREAK INTOCHIPS CHARGE CHIPS AND 0.2 WT. % ALUMINUM OXIDE C¹² TO BRINKMANN MILLGRIND TO POWDER AND SCREEN TO −140 MESH

EXAMPLE 3 On-Mold Coating Method

[0054] A polished unsaturated polyester mold surface was heated to atemperature between 300° F. and 325° F. under medium-wave IR lamps at42% intensity, after which one of the aforesaid powders (A, B, C) waselectrostatically sprayed onto the interior wall of the mold with atriboelectric spray gun within 1 minute from the mold leaving the IRlamps to cause the interface powder particles to melt and form acontinuous coating lining the mold surface. For 2 minutes after theapplication of the powder, the powder coated mold was again placed underthe medium-wave IR lamps and heated to a surface temperature of about350° F., during which time the unmelted powder particles above theinterface powders were caused to melt and coalesce into the coating filmand cure the coating film to a thermoset state. Thereafter, the mold wasallowed to cool to ambient temperature. Subsequently, alternating layersof fiberglass matting and fill resin were applied to the exposed side ofthe cured powder coating film by hand lay-up and then the fill resin wasallowed to cure at ambient temperature. After fill resin hassufficiently cured, the resulting product was removed from the mold andtested. This procedure was repeated for each of the aforesaid powders(A, B, C) with the exception that powder (C) was post-cured after IRcuring with UV radiation by passing the mold under a gallium dopedFusion-V lamp for 1-3 seconds.

[0055] Performance properties of the individual coating powders (A, B,C) and the coating films formed therefrom are given below. Results A B CGel Time at 400° F. (sec) 11  9 10 Hot Plate Melt Flow at 44 45 70 375°F. (mm) Sintering Resistance at Good Fair Good 110° F. under 100 gweight for 12 hours MEK Resistance No Rub Off No Rub Off No Rub Off (50Double Rubs) 4-5 4-5 4-5 Smoothness (Orange None None None Peel)Porosity No Yes No Intercoat Adhesion No Blisters No Blisters NoBlisters (Boiling Water) 60° Gloss 89 89 91 20° Gloss 74 70 78 CoatingAdhesion Good Good Good (ASTM D-3359) Coating Flexibility Very Good VeryGood Very Good Xenon Arc Weathero- Excellent Not Tested Good meter (ASTMG-26-92A) No Observable Slightly Better (1500 hours) Deterioration ThanGel Coat

EXAMPLE 4 Comparison Between On-Mold Coating Powders Of Prior Art andInvention

[0056] The following ingredients were blended together in the samemanner as in example 2 to form two different on-mold coating powderformulations, one formulation (I) being made in accordance with thisinvention, and the other formulation (P) being made in accordance withthe teachings of U.S. Pat. No. 4,316,869. Parts By Weight Ingredients IP Unsaturated Polyester (from Example 1) 95 Aropol 7501 (UnsaturatedPolyester)¹ 80 Triallyl Cyanurate (Monomer)² 8 Isodiallyl Phthalate(Diallyl Ester Prepolymer) 5 20 Lupersol 231XL (Peroxide Initiator) 4.54.5 Surfonyl 104-S (Flow Agent) 1 1 Modaflow 2000 (Acrylic Flow Agent) 11 Moldwiz P-66 (Release Agent) 3 3 TR 93 TiO₂ (Pigment) 7 7

[0057] It was then attempted to apply each formulation to a mold surfacein the same manner as in example 3. However, it was found thatformulation (P) experienced severe blocking at room temperature, i.e.,after {fraction (1/2)} hour exposure to room temperature (about 72° F.)the powder particles turned into a non-fluidizable solid clump. Uponattempting to spray formulation (P) through the triboelectric gun afterbreaking up the blocked powders by mechanical agitation, the powdersstill jammed in the gun and had to be mechanically released in the gunby a jig wire in order to coat the mold surface. While the final filmproperties achieved after curing formulation (P) were only slightlyworse than those of formulation (I), formulation (P) due to itsextremely poor blocking resistance is entirely an unacceptableformulation for use in commercial electrostatic coating operations.

[0058] Performance properties of the individual coating powders (P, I)and the coating films formed therefrom are given below. Results I P GelTime at 400° F. (sec)  6 25 Hot Plate Melt Flow at 375° F. (mm) 55 74Sintering Resistance at 110° F. Good Very Poor under 100 g weight for 12hours Free Flowing Powder at Rm Temp. Yes No Solid Clump After ½ HourMEK Resistance (50 Double Rubs) No Rub Off No Rub Off Smoothness (OrangePeel) None None 60° Gloss 91 82 20° Gloss 80 76 Xenon Arc WeatherometerExcellent (ASTM G-26-92A) (1500 hours) No Observable Deterioration

[0059] From the foregoing it will be seen that this invention is onewell adapted to attain all ends and objects hereinabove set forthtogether with the other advantages which are apparent and inherent.Since many possible variations may be made of the invention withoutdeparting from the scope thereof, the invention is not intended to belimited to the embodiments and examples disclosed, which are consideredto be purely exemplary. Accordingly, reference should be made to theappended claims to assess the true spirit and scope of the invention, inwhich exclusive rights are claimed.

What is claimed is:
 1. A method for on-mold coating a molded article inan open mold, comprising: a) providing a thermosetting unsaturatedpolyester coating powder composition which consists essentially of anunsaturated polyester resin, a copolymerizable cross-linking prepolymer,and a thermal initiator, with the proviso that the composition isessentially free of a copolymerizable cross-linking monomer; b) applyingsaid coating powder composition, which becomes the outer skin of themolded article, onto a shape-imparting mold surface; c) heating saidpowder coated mold surface to a temperature sufficient to flow andcoalesce the coating powder into a substantially continuous coating filmand effect cure, with the temperature being below the mold deformationtemperature; e) applying a fill resin, which constitutes the bulk of themolded article, onto said cured powder coating and allowing the cure ofthe fill resin to advance sufficiently until said powder coating filmand fill resin are integral; and, g) releasing said finished coatedarticle from said mold.
 2. The method of claim 1 , wherein said coatingpowder composition has the further proviso that either said unsaturatedpolyester resin possesses an active hydrogen, or said powder compositionfurther consists essentially of a photoinitiator, or both.
 3. The methodof claim 1 , wherein said coating powder composition further consistsessentially of a cure catalyst.
 4. The method of claim 1 , wherein saidcoating powder composition further consists essentially of a moldrelease agent.
 5. The method of claim 1 , wherein prior to step b) themold surface is preheated to a temperature sufficient to flow andcoalesce the coating powder into a substantially continuous film liningthe mold surface as the powder strikes the mold surface during step b).6. The method of claim 1 , wherein said mold is a plastic mold.
 7. Themethod of claim 1 , wherein said fill resin is an unsaturated polyesterfill resin.
 8. The method of claim 1 , wherein said fill resin isadmixed with glass fibers.
 9. The method of claim 1 , wherein the bulkof the article is formed in step e) by successively applying and curingas needed layers of fill resin and glass fiber matting over said curedpowder coating.
 10. The method of claim 1 , wherein said coating powdercomposition consists essentially of an unsaturated polyester resincontaining active hydrogen atoms, a copolymerizable unsaturatedprepolymer, a thermal initiator, a cure accelerator, and a mold releaseagent.
 11. The method of claim 10 , wherein said unsaturated polyesterresin is formed by reacting an unsaturated dicarboxylic acid oranhydride thereof selected from the group consisting of fumaric acid andmaleic anhydride, with an active hydrogen containing diol at leastcomprising cyclohexane dimethanol, along with minor amounts of aromaticdicarboxylic acid or anhydride thereof at least comprising phthalicanhydride and an aromatic diol at least comprising hydrogenatedbisphenol A
 12. The method of claim 1 , wherein said coating powdercomposition consists essentially of an unsaturated polyester resin, acopolymerizable unsaturated prepolymer, a thermal initiator, aphotoinitiator, a cure catalyst, and a mold release agent.
 13. Anon-mold powder coating composition, which composition is a film-formingblend in particulate form that consists essentially of: a) anunsaturated polyester resin; b) a cross-linking unsaturated prepolymer;c) a thermal initiator; and, d) a mold release agent, with the provisosthat: I) said composition is essentially free of a cross-linkingmonomer, and ii) either said unsaturated polyester resin contains atleast one active hydrogen atom, or said blend further consistsessentially of a photoinitiator, or both.
 14. The composition of claim13 , wherein said blend further consists essentially of: e) a curecatalyst.
 15. The composition of claim 14 , wherein said unsaturatedpolyester resin contains maleate or fumarate unsaturation and an activehydrogen selected from an allylic, benzylic, cyclohexyl, tertiary alkyl,and malonyl hydrogen, said copolymerizable unsaturated prepolymer is andiallyl ester of an aromatic dicarboxylic acid, said initiator is aperoxide, and said catalyst is cobalt salt of a fatty acid.
 16. Thecomposition of claim 14 , wherein said composition contains aphotoinitiator and said unsaturated polyester resin contains maleate orfumarate unsaturation and is free of active hydrogen atoms, saidcopolymerizable unsaturated prepolymer is a divinyl ether urethane, andsaid catalyst is a cobalt salt of a fatty acid.
 17. An on-mold coatedarticle formed by the method of claim 1 .
 18. A heat sensitive plasticmold having-the coating powder of claim 13 coated and cured thereonwithout causing significant thermal damage to the mold.
 19. A heatsensitive plastic mold having the coating powder of claim 14 coated andcured thereon without causing significant thermal damage to the mold.